1. Field of the Invention
This invention relates to a laser light irradiation apparatus, which irradiates laser light onto living tissues of an animal such as a human body for use in making an incision, vaporization of the living tissues or a thermal therapy and in case of widening a narrow path of the living tissues such as a stricture part caused by cholesterol formed in the blood vessel of the human body.
2. Prior Art
Medical treatments such as incisions of living tissues of animal organisms by irradiation with laser light are conspicuous due to the ability of such irradiation to provide hemostasis.
It had been the conventional method that the laser light was irradiated from the fore end of an optical fiber which is held out of contact with the living tissues. This method, however causes severe damage to the fore end portion of the optical fiber. Therefore, a method using a contact probe has been utilized as discussed below.
First, laser light is transmitted into an optical fiber, whose fore end portion is adjacent to treated living tissues. Next, the laser light fed out from the optical fiber is fed into an emitting probe, which is brought into or out of contact with the living tissues. Then, the laser light is emitted from the surface of the probe and irradiated against the living tissues. In this case, the probe should be brought into contact with the living tissues (hereafter "living tissue" is sometimes expressed by "tissue" only).
The inventor developed many kinds of contact probes which are utilized for various purposes.
When the contact probe of this type above described was used in the prior art, the fore end of an optical fiber was located so as to be apart from the back end face, that is an impinging face, of the probe. In this case, a physiological salt solution or pure air was passed through a gap formed between the optical fiber and a holder supporting the optical fiber, and through a space formed between the impinging face of the probe and the fore end of the optical fiber. Then, although the laser light having high power level impinged on this impinging face of the probe, this face could be cooled due to the passing of this fluid. Thus the damage of this face was prevented. Further, entry into the gap by pieces of living organism, a blood flow and the like, which might have occurred during a medical operation, could be prevented due to the passing of this fluid.
On the other hand, the inventor proposed, in Japanese Patent Application No. 63-171688, a laser light medical treatment equipment for burning off a stricture part caused by cholesterol formed on the inner wall of a blood vessel.
Before this invention, that is Japanese Patent Application No. 63-171688, for the treatment for the stricture part, a heat wire probe was inserted into the stricture part. Then, since the heat wire probe was heated as a whole, a normal blood vessel other than the stricture part could be damaged. Therefore, in order to prevent the normal blood vessel from being damaged, the laser light medical treatment equipment of this invention was proposed. According to this equipment, a laser light emitting probe is progressed through the blood vessel to a location before the stricture part formed in the blood vessel, and the laser light is emitted so as to irradiate only the stricture part, which is beyond the probe.
Further, lately, a localized thermal therapy is drawing special attention as a carcinostatic therapy. According to this method, cancer tissues are destroyed by keeping the cancer tissues at a temperature of about 42.degree.-44.degree. C. for 10-25 minutes by laser light irradiation. The effectiveness of this method has been reported by the inventors in the bulletin of Japan Society of Laser Medicine, vol. 6, No. 3 (January 1986) pp. 71-76 & 347-350.
On the other hand, considerable attention has been paid to laser-chemical therapies including the method reported in 1987 by Dougherty et al of the United States. According to this method, 48 hours after an intravenous injection of a hematoporphyrin derivative (HpD), weak laser-light such as argon laser or argon pigment laser is irradiated against a target area of the treatment, whereupon oxygen of the primary term which has a strong carcinostatic action is produced by HpD. There have been published various reports in this regard, including one in the bulletin of Japan Society of Laser Medicine, vol. 6, No. 3 (January 1986), pp 113-116. In this connection, it has also been known in the art to use "pheophobide a" as a photo-reactant. Further, recently, YAG laser has been put into use as a laser-light source.
In the above mentioned medical treatment, it is important that the laser light be irradiated uniformly for the cancer tissues and, in case of the thermal therapy, it is particularly important that the cancer tissues are heated uniformly.
Further, for heating the tissues uniformly, the inventor disclosed in Japanese Patent Application Laid-Open No. 63-216579 that an apparatus has plural number of laser light emitters and equipment for adjusting the power level of the laser light impinging into the emitters.
If laser light is irradiated against the tissues from an optical fiber directly or through the intermediary of a contact probe, the power level of the laser light irradiated against the tissues is the largest at a center position of an irradiated area on the surface of the tissues. The center position is contacted by the center of the optical fiber or that of the contact probe, then the power level decreases at positions on the surface of the tissues away from the center position.
For example, as shown in FIG. 28, when the laser light is irradiated against the tissues M with a contact probe P, the temperature distribution of this figure shows a distribution which is similar to a normal distribution. If the power level of the laser light is raised, the size of this temperature distribution is also enlarged to be a substantial similar figure. However, if the power level of the laser light is increased to an excess level, the tissues corresponding to the peak of the temperature distribution are damaged seriously. Accordingly, it is impossible that enlarging an irradiation area be carried out by only adjusting of the power level of the laser light.
Therefore, it is difficult to irradiate the laser light uniformly, and particularly more difficult to irradiate the laser light uniformly against the tissues having broad area. Accordingly, within the limit of the predetermined power level of the laser light, laser light irradiation against each small part of the tissues must be repeated many times in order to carry out the irradiation against all of the broad area the treated tissues. As a result, a medical operation can not be carried out quickly.
Under these circumstances, as described before, the inventor proposed in Japanese Patent Application Laid-Open No. 63-216579 providing a plural number of probes as the laser light emitters such that the laser light is irradiated from each probe simultaneously.
Although the laser light can be irradiated against the tissues having a broad area to some degree by provision of the plural number of laser light emitting probes, the necessity of the probes causes a problem as discussed below.
For forming the uniform temperature distribution on the irradiated tissues, the probes should be located at precise positions respectively in order to uniformly contact the tissues. Therefore, the medical operation can not be carried out quickly due to difficulty in precisely locating the probes. On the other hand, since each optical fiber should correspond to each probe, the size of the apparatus is large. Accordingly, this apparatus can not be used for a medical treatment in a narrow path in the tissues such as a catheter in a blood vessel.
On the other hand, in case of a treatment for a so-called angioplasty, which means burning off the stricture part formed on the inner surface of the blood vessel to widen the inside of the blood vessel, as described before, the inventor proposed the laser light irradiation probe. In this case, the probe can be used instead of the conventional heat wire probe and is inserted into the blood vessel along the flexible guide wire, which was inserted into the blood vessel previously. Further, in an embodiment of this proposal, in order to prevent the guide wire from being damaged by the laser light irradiation, the guide wire is placed so as to be deflected from the axis of the probe.
As shown in FIG. 29, deflection of the guide wire in relation to the axis of the probe causes the following problem. When a probe P is inserted in the blood vessel until the probe P reaches a bend in the blood vessel, due to the deflection of the guide wire, the probe P should be forced to be progressed further in the blood vessel against the original bending of the vessel. Therefore, the bending manner at this original bending of the blood vessel is changed to another bending manner. In this case, when the laser light is irradiated against the stricture part m, there is the fear of breaking of the wall of the normal part of the blood vessel BV other than the stricture part m or so-called perforation there.
The energy distribution of the laser light irradiation from the probe and the above mentioned temperature distribution shown in FIG. 28 have a common characterization. That is to say, in this energy distribution, there is a peak at its center while the level is gradually lowered at the both sides. Therefore, while the center of the stricture part m is completely burnt off, the inner wall of the stricture part m away from the center often still remains without being burnt off. Accordingly, the power level of the laser light should be raised in order to burn off the whole stricture part completely. However, if a normal part of the inner wall of the blood vessel faces the center of the emitting face of the probe due to the bending of the blood vessel, there is a risk that the normal part is burnt.
On the other hand, in the conventional apparatus where the fore end of the optical fiber is located so as to be apart from the back end face of the probe, there are the following problems:
(1) When the laser light impinges on the back end face of the probe from the fore end of the optical fiber, the impinging face of the probe is heated, thus; the cooling fluid should be supplied as explained before. Then, an equipment for supplying the fluid is necessary, resulting in an expensive apparatus. Further, a path of the fluid should be provided, thus the apparatus can not be designed so freely. The cooling fluid might flow into the tissues of a human body, thus; a bad effect is caused for the human body.
(2) The space formed between the fore end of the optical fiber and the back end face of the probe cause a power loss of the laser light. Accordingly, in order to compensate for this power loss, a large sized laser light generator is required.
(3) The cooling fluid is, as described before, also used for cleaning the fore end face of the optical fiber and the back end face of the probe. However, they are not cleaned sufficiently with the fluid, thus, damage caused by incomplete cleaning can not be prevented completely.